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Split Second MAF (laptop version) Write-up

I took the plunge and bought the Split Second MAF conversion kit with their PSC1-4, laptop programmable signal calibrator, along with their optional intake air temperature sensor. Split Second does not have a specific E28 M5 fuel map available. Unfortunately, no one on any of the E28 M5/S38 forums responded to my posts for a copy of their fuel map. So, I didn't have a good starting point but the system was easy enough to adjust to get a drivable base fuel map that got me to the dyno shop. Mark has also been extremely patinet and helpful in answering all of my questions. Following are the major points of interest:

Engine Modifications-
Besides the new MAF conversion, Conforti chip, and exhaust cam gear, my engine is stock with 180k miles and no renewed parts. I recently removed the injectors for cleaning by a local Dr. Injector franchise but did not notice any difference in drivability afterwards. The flow test revealed a couple of injectors were about 6.5% low in flow compared to the highest flowing injector. After the cleaning all injectors were within 1.5% of each other.

Drivability-
Overall, my car runs fairly smoothly, as if it still had the AFM installed but revs more quickly with better torque from idle to redline. I have some very minor hesitation when I accelerate aggressively off idle. After re-installing the AFM, I noticed that the hesitation was always there but is a little more perceptible with the MAF. Otherwise, acceleration is smooth with power coming on seemingly quicker. The engine will rev very quickly to about 3.8k, and then rev similarly to when the AFM is installed to redline. I am hopeful that additional fine tuning of the fuel map will eliminate most of the hesitation. Intake noise is slightly higher but probably not noticeable to anyone else. I'm using the factory air box modified with a larger opening as the factory air filter has a lot of surface area compared to some of the cone filters included in cold air intake kits. With the optional intake air temperature sensor, I get pretty close to the same fast idle characteristic as it had with the AFM, though I think fast idle isn't quite as high but will have to wait until winter to know for sure. Idle quality is typical M5, a little lopey with no improvement over the AFM, though it was never too rough (for me). Though the MAF doesn't make my M5 feel like a new car, it is more fun to drive around town with the noticeable torque gain and quicker revving engine. Switching back and forth a couple of times between the MAF and AFM, for comparison, reveals enough of an improvement that I prefer the MAF.

MAF Setup-
First of all, if you decide to get a Split Seconds PSC set up, I would highly recommend that you spend the extra $50 to get the auxiliary input option which allows you to record up to 4 data points, like O2 sensor voltage, manifold pressure (for turbos), etc. I was not aware of this option until after my purchase. I was informed that the option cannot be retrofitted. The PSC1 does, however, have the capability to record engine rpm, MAF voltage and the fuel map value that is used to modify the output voltage to the DME. With this in mind, I cut into the PSC1's wiring to add spade connectors to the MAF signal and airflow to Motronic wires so that I can disconnect the MAF signal and connect the AFM signal to the MAF input into the PSC. This allows me to record the AFM's signal when I put things back to stock. To be able to reinstall the AFM, I fabricated an adapter plate that allows me to reinstall the AFM to the factory air filter box, as I cut a larger opening for the MAF. The rest of the MAF installation is per Split Second's instructions. One thing that isn't clear is where all of the ground wires for the new equipment should be connected. I think I noticed a little better performance with all grounds connected to the AFM sensor ground compared to connecting to one of the large DME ground wires.

MAF Tuning-
Split Seconds pre-installed fuel map was extremely rich and could not be used. By monitoring the air/fuel meter, it was relatively easy to get a base fuel map that would run acceptably but I knew I needed some dyno time to be sure I wasn't running lean. Once I figured out that I could record the AFM's signal, I made the wiring modifications, reinstalled the AFM and recorded an idle voltage of 1.0V and a WOT voltage of 4.2V. I was pleasantly surprised to find out that the MAF has the exact same output range of voltage from idle to WOT. After my dyno session, I had the 2,500 rpm to redline dialed-in with an air/fuel ration of about 12.5:1. Since then, I have made 8 different fuel maps with several iterations in each trying to optimize off idle acceleration and cold start drivability. After several weeks of tuning, I am pretty close but there is an infinite amount of adjustability with the PSC.

Other things-
I noticed that the AFM has a rounded rectangular entry nozzle which I assume reduces turbulence. I plan to do a little searching to see if I can find something similar for the round MAF. Is the MAF conversion worth it?...The power and torque increases are significant but not astounding. I was hoping for at least 20 rwHP. But because of the tunability, the knowledge I have gained and the fun I have been having with experimenting and fine tuning, I would do it again even if I was guaranteed only 14 rwHP. The entire MAF conversion kit cost me $770 (including a 10% discount) delivered plus another $315 for dyno tuning. So far, it appears that my "normal city" and highway mileage have not changed, 14 and 22 MPG, respectively, though I'll have to stop with the fine tuning for another tank or two to be sure.

I have read that at WOT, the DME ignores airflow. This may be a simple mistake as I would agree that the O2 signal is ignored but not airflow. The stock AFM is sized to measure the full airflow that the engine can pump as I have recorded the voltage ranges produced by the MAF and AFM during dyno runs and they are identical. RPM by itself is not a very good indication of airflow or engine load. Airflow will differ greatly depending upon the conditions on the engine. For example, you could be traveling up hill in a lower gear, versus highway cruising in a medium gear and be at the same rpm but very different airflow/engine loads. At the instant you go WOT, the fuel requirements are different. Even if the DME were to take this into account and is conservative across the rpm range, it seems like there would be a scenario where too much fuel is added hurting performance. I acknowledge that Iím no expert but it doesn't make sense for the DME to base fuel control solely on rpm at WOT when it can get an airflow signal to determine how much fuel is needed. Also, the real world reason why I believe this is that I was able to change the air/fuel ratio at WOT via the PSC1 during my dyno runs. My recorded dyno runs show this. Mark at Split Second has also told me that O2 is ignored, not airflow. I donít mean to offend anyone but want to share my experience.

Re: Nice write up!

I'm completely stock right now and really appreciate your write-up. Down the road I'm planning on pulling every last bit of hp I can out of my e28 M5. Given all the options I'm pretty much starting a library of info. Thanks for the addition :)

Dan, great write=up. I'm guessing, but one >>>

possible reason you didn't get any responses to your querry about a fuel maps might be, you're the first to have this new SS MAF setup, at least on this forum. One thing I don't understand is why SS doesn't offer an inexpensive data logger to rent to aid in the tuning. From your description, it appears one would only have to pick off the voltage from the AFM and the RPM values. But then one could also tap into the AFM signal and record the various voltages against RPM to ue as a base starting point.

The AFM signal being ignored above a certain RPM value or at WOT is an urban legend that has been propogated by the Probst book. Apparently the earlier Bosch L-Jet system did in fact function in this manner. Somehow this made it's way into the Motronic section of the book. Jim Conforti made mention of this several years ago on one of the lists.

Thanks for providing the excellent writeup about your experiences with this new MAF conversion.

Good stuff Dan

Interesting write-up and shows yet again the AFM doesnít restrict power as much as people generally believe. I was keen to replace mine on my M535 (same AFM as M5) till I investigated it and found the pressure drop across it is only 8Ē water a full power. Iím still thinking about the subject though.
You are correct about the AFM is NEVER ignored at anytime period, Iím surprised you say you only get 4.2V output at WOT. If the AFM is nearly fully open it should be closer to 4.8/9Volts.
Even the 2valve 535 head at around 5500rpm can suck hard enough to take it to 4.8V a good M5 engine should be able to ďsuckí the flap fully open thus produce 4.9 + output. This is when you know your engine really is ready for something bigger because once it the AFM is fully open and you still Ďsuck harderĒ -to use crude terms Ė ,the pressure drop goes up. Maybe your spring is too tight.
The o2 sensor is ignored as soon as the TPS signals full throttle (which is actually 7/8 throttle). This can be shown if one drives the car while monitoring the 0/12v o2 signal on the diagnostic connector. It normally has a 50% duty cycle but as soon as WOT signal is registered goes to its default value of 12V.
Throttle response is definitely an area the AFM can be improved in.
Let the board know of any other observation you make on your new setup.

Re: Great write up....

The local dyno shop is RPM in Kirkland, WA. I believe they have a Dynojet 224x. I am using the stock O2 sensor though I have read and heard that Innovate Motorsports has a wide band kit with handheld readout that can synthesize a narrow band signal for the DME via an adaptor. It's also supposed to have data logging capabilities! I'm going to check this out.

Re: Good stuff Dan

It is interesting that the airflow signal was 1V at idle and 4.2V at WOT at peak power for both the AFM and MAF. This kind of indicates that the AFM is probably measuring accurately. Do you have any voltage readings for the AFM relative to flapper position?

It would seem logical that full open of the flapper should be at or very close to 5.0V. If this is the case, you would be right about the AFM still having capacity and therefore other parts of the intake or exhaust systems are restricting flow. The dyno technician noted that he thought that the engine wanted to make power but hit sort of a "wall", most likely an exhaust restriction.

One thing I forgot to note is that Split Second's R4 software map is set up with fixed rows of RPM's at 500rpm intervals and columns of load voltages from 1 to 5V at .1V intervals. The interval of load voltages seems fine but it would be great if the RPM rows were either adjustable or had smaller intervals, like 100rpm. This would allow more fine tuning off idle.

Re: Dan, great write=up. I'm guessing, but one >>>

Split Second's PSC1 can log data. It can record rpm, MAF voltage and the map value that is used to modify the MAF signal. For $50 at the time you order, you can have the capability to log four auxiliary inputs like O2 signal. It would be a great set-up to record a wide band O2 along with the base PSC1 data. As a minimum, with the auxiliary input feature and even a stock O2 sensor, you would have a very good set-up for tuning. You then could get by without spending the big dollars on dyno time to ensure you don't run lean. It is very difficult to look at the A/F meter and the laptop while your driving to see where you are operating on the fuel map. You are right about recording the AFM signal, as this is what I did with the PSC1 to help figure out a base line map.

I'm glad to hear that I'm not off base about the airflow signal not being ignored.

I've been thinking of that wbo2 also....

from innovative. It seems like the best deal out there. If you do it, don't forget to do another write up :) I've been thinking of going with a Maxx alpha-N set-up, the only concern I've had is the lack of basemaps but it seems like that wasn't too much of a problem for you which is promising.<img src="http://home.comcast.net/~wong.andrew/pics/sig.JPG">

Re: I've been thinking of that wbo2 also....

Prior to my decision to get the SS MAF system, I almost bought a Maxx Alpha-N. I talked with John, a US rep who has an E30 M3, and they have a "money back" type of gurantee but in the end the additional $300+ for the Alpha-N tipped the scale for me. I recently met another E30 M3 guy who has a highly modified 2.5L S14 with the Alpha-N and he is making 245 rwHP! One thing the Alpha-N has over SS is that you can define the rpm columns compared to set rpm's with SS. This allows fine tuning around specific rpm problem points. And of course, you don't have any obstructions in the intake.

Re: Good stuff Dan

Dan the AFM just uses a simple voltage divider setup it gets a regulated 5V reverence from the ECU then outputs a voltage via the divider between about 1V to 4.9V depending on the position of the flapper.
4.2V is about only a ĺ open flapper from memory (itís a while since I measured mine) but you can easily check for yourself by turning on the ignition with the AFM connected (that will provide it with the 5V ref) put your DVM on the output signal and physically move the flapper with a stick and note the position /volts etc.
There was a difference between the early ones and late being log/linear etc but the fully open voltages about the same.
Exhaust backpressure build up at full power maybe stopping you getting a full inlet charge on the overlap.
Measure your flapper position as above Iíd be interested to know the results-maybe you can get more power yet.

Airflow

Read all the recent posts with great interest as I am thinking of going down a similar route. Great info all round.

I have been investigating air flow restrictions on the M635 head to see how I can make mine breath better. The following link has given me a head start - http://www.metricmechanic.com/M3Engine.pdf.

It has a great deal of info on the air flow characteristics of the E30 M3 head which has 26mm inlet tracts and 46mm throttle bodies with 37mm inlet valves. These dimensions are EXACTLY the same as my M635 head (I know the cam durations are different). Metric Mechanic claim (with some good back up info) that it is the inlet tract on the head that limits air flow, not the throttle bodies or the air box. They even port the inlet tract to 31mm diameter without making a change to 48mm throttle bodies.

I would suggest that the air flow meter capability on an M6/M635 should never reach fully open (apart from transients) as I can't see BMW designing a flow meter that reached fully open before full air flow was acheived. They would always build in some margin (but not in there inlet tracts it would appear)

Hence maybe why you are seeing 4.2v at full air flow. i.e. there is capacity left in the breathing capability. With you getting 4.2 v with the MAF this demonstrates to me that it IS the inlet tracts that are the restriction. MM look at exhaust flow but this is 120% against a normal design of 85% and so there should not be a restriction here.

My route to more power is perhaps opening the inlet tracks to 29mm and creating the same crossectional area of the 46mm throttle bodies hence maximising the throttle body capability. A schrick 272 inlet cam would then encourage more air flow. Exhaust side to remain standard. Then off with Alpha N or SS to give the tunability.

With the increased breathing of the schrick cam I would hope that the air flow meter capability is not exceeded as it isn't a radical cam profile. Again your info stating 4.2v at WOT is invaluable as it gives me the confidence that there is still some capability left in the air flow meter and hence I can do the head porting (spare head), cam install and then engine management progressively and not in one go (ouch on the £'s). I know mine is a M635 but I would welcome confirmation that the inlet tracts on an M6 are 26mm and inlet valves are 37mm. The only concern I have now is that the M635 may use the same air flow meter. M635 delivers 286bhp against 256bhp for the M6 and hence my flow meter MAY be aproaching max open now.

Phew - anyway my thoughts only as I have been trying to do a lot of research before going down the engine modifying route. Open to be corrected on any of the above or for further info on air flow characteristics.

See post above on air flow. (eom)

Great write up! There's a reason that all new BMWs

...use MAF's in favor of the obsolete technology of the AFM! Glad to see that someone has put this to the test and has so articulately and comprehensively written it up. BTW, your horsepower gains are extremely significant, so don't feel disappointed about that!

Similar experience w/ old version

My impressions of my car's performance after running the SS MAF kit w/ the 4-knob controller for 4 months are very similar to Dan's - definitely more torque and quicker response as noted by butt dyno (have a JimC chip but otherwise stock). I have not switched the AFM and MAF back and forth, but that is a great data point, as of course is the dyno. It is not our imagination. I need a brake upgrade next, the car really hustles.

Dan's hp/torque gains on dyno are similar to SS's data on website. Tough to get those kind of gains with any other "simple" mod. I continue to have no problems whatsoever. I am sure others will appreciate Dan's pioneering work here w/ the laptop version maps. If you are less inclined to spend time tweaking, the old version works fine and no dyno is needed (altho if you log the O2 signal the same may be true for the laptop version).

I agree with Dan that there is still a bit of a flat spot at 4000-ish rpm when accellerating from a stop. Mine was more pronounced w/ the AFM, and there were more flat spots. Now I just have the one and it is minor, and not always there.

Split Second MAF (laptop version) Up-date

I talked with Mark (at Split Second) further on how to fine tune their system. Since I don't have the auxiliary input for data logging, I had a friend help me drive my car while I watched the A/F meter and the fuel map on my laptop. From this I was able to closely figure out where I was running too rich, causing the minor hesitation. I thought I was still not giving it enough gas under acceleration. I was basically running too rich in nearly all lower rpm settings. I think the biggest help was that I had the mixture at idle too rich. Leaning it out at idle and at certain load/rpm combinations has made a huge difference. Though idle quality is the same, my car is smooth in all acceleration situations. It is much better than the AFM now! It also seems like there isn't a step at 3.8K rpm anymore. It just pulls strong all the way to redline and it does it very quickly.

In regards to fuel maps, I'm willing to share my maps with any non-Split Second individual who is interested. I probably won't post them for general download.

Re: Split Second MAF (laptop version) Up-date

Sounds good Dan I wonder how much of the improvement in general is down to the tighter programming/control of the A/F ratio with the MAF over the AFM.
What is the output voltage of the MAF at full power now?
Iím interested because your work has resurrected my interest in my own project to replace my AFM or improve it more.

Re: Split Second MAF (laptop version) Up-date

I think the improvements in drivability over stock are all due to the adjustability of the programmable PSC1. The maximum voltage that I have seen from the MAF is 4.2 volts. All of the tuning adjusts the signal that the DME sees based upon MAF signal at a given rpm. Unless I change some physical aspect of either the intake (porting/polishing) or the exhaust (high flow cat), I won't see any increase in air mass that the MAF is measuring.